Balancing strength, modulus, and biocompatibility in a novel oxygen-containing β-type titanium alloy

Reducing the elastic-modulus mismatch between metallic implants and cortical bone remains a central challenge in orthopedic materials design. We report the development and evaluation of an oxygen-containing β-type titanium alloy, Ti–12Zr–6Nb–2Mo–2Sn–1.2O, engineered to combine high strength, ultralow modulus, and excellent biological performance. The oxygen was added to suppress the martensitic transformation and increase the strength of the Ti–12Zr–6Nb–2Mo–2Sn alloy. X-ray diffraction confirmed single-phase β stability without martensitic transformation across annealing treatments (1173 K, 60 s–1.8 ks). Texture and EBSD analyses revealed progressive weakening of the {110}⟨001⟩ with recovery and recrystallization. Tensile tests showed tunable responses: a favorable balance of low modulus (41 GPa) and high strength (>1000 MPa) at short annealing times, and increased ductility after prolonged annealing. Surface characterization indicated similar wettability and moderate roughness compared with cp-Ti; electrochemical tests confirmed stable passive-film formation and corrosion resistance. In vitro assays revealed enhanced fibroblast proliferation but reduced osteoblast adhesion relative to cp-Ti, indicating cell-type-dependent interactions. In vivo subcutaneous implantation in rats demonstrated tissue compatibility comparable to cp-Ti, with mild inflammation, successful regeneration, and normal hematopoiesis, albeit with slightly higher mast-cell degranulation. Collectively, Ti–12Zr–6Nb–2Mo–2Sn–1.2O is a promising low-modulus β-Ti alloy for load-bearing orthopedic implants; oxygen addition synergistically stabilizes the β phase and enhances mechanical performance while maintaining biocompatibility.